Cells of Catharanthus roseus (L.) G. Don were maintained and sub-cultured in the absence of NaCl (control) or were sub-cultured for 7 days in the presence of 50 ("50") or 100 ("100") mM NaCl, or were maintained and sub-cultured for 8 months in the continuous presence of 50 mM NaCl ("50T" or salt-adapted cells). Exposure to salt treatment reduced growth in a concentration-dependent manner. Salt-treated cells strongly accumulated Na + and, to a lesser extent, Cl -. However, no significant change in Claccumulation was observed in 50T cells.Salt progressively increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities whereas a strong increase in catalase (CAT) activity was only obtained in 50 and 50T cells. SOD activity was lower in 50T than in 50 cells, whereas the opposite was observed for APX activity.After native polyacrylamide gel electrophoresis (PAGE) analysis, five SOD isoenzymes were detected and the increase in SOD activity observed in salt-treated cells seemed to be mainly due to isoenzymes (SOD 1, 2 and 3). Three APX isoenzymes (APX 1, 2 and 3) were detected markedly, especially in salt-adapted cells. Salt strongly induced CAT 2 isoenzyme in 50 cells and CAT 1 isoenzyme in 50T cells. These data suggest that salt treatment provoked an oxidative stress in C. roseus cells, as shown by the increase in lipid peroxidation, in spite of the induction of antioxidant enzymes. This increase in lipid peroxidation was paralleled by a rise in lipoxygenase (LOX) activity.Increases in antioxidant activities could also be a response to the cellular damage provoked by NaCl. Probably, this increase could not stop the deleterious effects of salt, but reduced stress severity thus allowing cell growth to occur. On the other hand, and although no JA measurements has been carried out, the antioxidant enzymes could me mediated, at least 3 partially, by an LOX-mediated JA increase in salt-treated C. roseus cells. SALEM: Please penser si on laisse ce paragraph or no

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The amino acid sequence of the heme-binding domains of rat liver cytochromes b, from outer mitochondria1 membranes and from microsomes has been determined by a combination of automatic and manual degradation of fragments generated by trypsin digestion and by cleavage at tryptophan. Tryptic peptides were separated by high-pressure liquid chromatography.The sequence of microsomal cytochrome b, is identical with the one published by 0201s and Heinemann after completion of this study [Biochinz. Biophj,~. Artu (1982) 704, 163-1731. The sequence of outer membrane cytochrome hs differs from the microsoinal one at 38 positions out of 92. There are 40 positions invariant between this sequence and the eight microsomal sequences published thus far. The non-conservative substitutions are located at the surface of the known three-dimensional structure of calf microsomal cytochrome h5 except for the substitution of histidine-I5 by arginine.This paper brings the final proof that two iso-cytochroines b5 exist in the same cell. Their high degree of similarity as well as their differential cellular localization raise some questions which are briefly discussed.

Flavocytochrome bz from baker's yeast is a bifunctional tetrameric protein which carries two prosthetic groups, FMN and heme, per subunit of M, 58000. The amino terminus of the subunit is wrapped around the heme and constitutes the so-called cytochrome bz core (Mr 11 000), homologous to cytochrome bs. It has been shown in the past that a number of proteases (yeast proteases, chymotrypsin) preferentially cleave the peptide chain at a point situated much further down the polypeptide chain than the C terminus of the heme-binding domain. Some enzymatic parameters are concomitantly modified, but not the quaternary structure. This paper describes the conditions for selective proteolysis of intact flavocytochrome bz and of its various previously studied stable nicked forms by the protease from Staphylococcus aureus V8. Successive attack by a combination of two proteases is also described. We have established the amino acid sequence of the area where proteolytic attack takes places, and shown that chymotrypsin and S. aureus protease open only one bond, whereas yeast proteases remove five residues from the central part. The various nicked forms, some of which have lost up to 16 amino acid residues, have been enzymatically characterized.These and previous results lend support to, but do not prove, the idea that the flavodehydrogenase part of flavocytochrome h2 may be composed of two domains, linked by the region accessible to proteases. That area might constitute a hinge or rather a clasp between the domains.